1. Field of the Invention
The present invention generally relates to an ad-hoc sensor network. More specifically, the present invention relates to a system and a method enabling nodes forming an ad-hoc sensor network to transmit data using a minimum power.
2. Description of the Related Art
In a general communication system, data is transmitted and received between a mobile element and a base station. The mobile element and the base station directly transmit and receive data without having to pass through other nodes. In contrast, when data of a certain node is transmitted to a base node in an ad-hoc sensor network, other nodes are not available. Referring to FIG. 1, the configuration of the ad-hoc sensor network is described below. The ad-hoc sensor network consists of an operator 100, a base node 102, and a plurality of nodes as shown in FIG. 1.
The operator 100 requests the base node 102 to collect necessary data. The data requested by the operator 100 relates to information on temperature of the environment around a sensor field 104. The base node 102 requests the requested data to each node located in the sensor field 104, and forwards the data received from each node to the operator 100. Each node collects the data requested by the base node 102, and transmits the collected data to the base node 102. Nodes located within a certain distance from the base node 102 transmit the collected data directly to the base node 102. Other nodes located outside of the certain distance from the base node 102 transmit the collected data to the base node 102 via neighbor nodes of the base node 102, not directly to the base node 102, so as to minimize the power consumed for the data transmission. The distance from the base node 102 to a node is directly proportional to the power consumed by the node to transmit data. Accordingly, the nodes out of the certain distance from the base node 102 transmit the collected data via a plurality of other nodes so as to reduce the power consumption for the data transmission. Hereinbelow, a node relaying data of another node refers to a relay node. The relay node traits its collected data directly to the base node 102 or via other relay nodes.
FIG. 2 illustrates a node determining a relay node for transmitting the collected data to the base node. The node transmitting the collected data refers to a start node 200. The start node 200 transmits the collected data to the base node via relay nodes. It is assumed that the node 204 is a relay node which relays the collected data of the start node 200 to the base node.
The start node 200 determines whether to use the node 202 as a relay node or not. Specifically, the start node 200 needs to determine whether to use both of the nodes 202 and 204 or to use the node 204 alone, to transmit the collected data to the base node. The start node 200 determines the relay node based on the power consumption for the data transmission of each node 202 and 204. In general, the power consumed for the data transmission is directly proportional to the square of the distance between nodes transmitting and receiving data with each other.
Provided that the power consumed to transmit data from a node A to a node B is Γ(A, B), the power consumed to transmit the collected data from the start node 200 to the node 204 is Γ(200,204) and the power consumed to transmit the collected data from the start node 200 to the node 204 via the node 202 is Γ(200,202)+Γ(202,204). The start node 200 compares Γ(200,204) with Γ(200,202)+Γ(202,204) and determines whether to use the node 202 as the relay node.
FIG. 3 illustrates another example of the start node determining the relay node. The start node 300 pre-stores the case when a certain node can be used as the relay node. If the node 302 can be the relay node, the start node 300 transmits its collected data to the nodes 304 and 306 located in the relay region 310, via the node 302.
Each node 300 to 308 is initially set to identify locations of itself and neighbor nodes. That is, each node can identify the location of the nodes capable of transmitting the data not via the other nodes. Hence, the start node 300 uses the node 302 as the relay node only when the start node 300 transmits data to the nodes 304 and 306 in the relay region 310. If the node 308, which the data is destined for, is out of the relay region 310, the start node 300 does not use the node 302 as the relay node.
As described above, the conventional routing method, that is, the method for determining the data transmission path, considers only the distance between the nodes. The distance is calculated using the location information of each node, and the power consumption for the data transmission is calculated using the acquired distance. The path having minimum power consumption is determined based on the calculated power consumption. However, it is disadvantageous to measure the power consumption based on the distance alone. For example, even if the distance is short, significantly more power may be consumed for the data transmission due to environmental factors.